Method of optimizing vehicle performance based on countershaft acceleration

ABSTRACT

The present invention provides a method of controlling input torque of a powered vehicle. The vehicle includes a transmission having an input shaft, an output shaft, and a countershaft. The method includes providing input torque to the input shaft, determining a rotational acceleration of the countershaft, and measuring vehicle speed. The method also includes determining a threshold based on the measured vehicle speed. The measured countershaft acceleration is compared to the threshold and the input torque is controlled based on the result of the comparison.

RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationSer. No. 61/532,707, filed Sep. 9, 2011, which is hereby incorporated byreference in its entirety.

FIELD OF THE INVENTION

The present invention relates to a method of optimizing vehicleperformance, and in particular to a method of optimizing vehicleperformance using countershaft acceleration.

BACKGROUND

Engine and transmission manufacturers continue to seek ways to improvefuel economy and vehicle performance in powered vehicle systems.Conventional vehicle transmissions include software or a control schemefor determining when the automatic transmission shifts from one gearrange (or ratio) to another gear range. This control scheme is commonlyreferred to as a “shift schedule” and is based on multiple factors,e.g., engine torque, vehicle speed, accelerator pedal position (i.e.,throttle percentage), transmission output speed, and tractive effort.Any given shift schedule for a vehicle balances fuel economy againstperformance.

In addition, engine and transmission manufacturers work together to forman integrated system that drives vehicle performance. For instance, anengine may produce different torque levels to drive a transmission basedon a specific driving condition. At a lower torque level, the vehiclemay operate with better fuel efficiency but with reduced performance. Ata higher torque level, the vehicle may perform better but consumes morefuel.

Many conventional vehicle setups control engine torque by monitoring avehicle's acceleration. The reason for doing so is because there is noeasy or convenient way to limit torque based on transmissionperformance. Most conventional transmission assemblies include a singlecenterline on which input and output shafts are disposed. The input andoutput shafts rotate at high speeds and accelerate/decelerate quicklysuch that it is difficult to control engine performance based on thesespeeds. Thus, engine torque is controlled by vehicle performance ratherthan transmission performance. However, integrating the engine andtransmission such that engine performance is controlled based ontransmission performance is desirable since the two assemblies areintegrated with one another for different vehicle setups.

Therefore, a need exists for optimizing vehicle performance bycontrolling engine torque based on a transmission characteristic.

SUMMARY

In an exemplary embodiment of the present invention, a method isprovided for controlling input torque of a powered vehicle. The vehicleincludes a transmission having an input shaft, an output shaft, and acountershaft. The method includes providing input torque to the inputshaft, determining a rotational acceleration of the countershaft, andmeasuring vehicle speed. The method also includes determining athreshold based on the measured vehicle speed. The measured countershaftacceleration is compared to the threshold and the input torque iscontrolled based on the result of the comparison.

In one form of this embodiment, the method further includes continuouslymeasuring countershaft speed with a speed sensor and calculatingcountershaft acceleration over a given time period. In another formthereof, the controlling step comprises limiting the input torque. Themethod can also include maintaining the amount of input torque providedto the input shaft. In addition, the method can include sending a signalto an engine controller to control the input torque. Alternatively, themethod can include repeating the comparing step until the countershaftacceleration is less than the threshold. In one aspect of thisembodiment, the threshold is determined from an acceleration curve basedon vehicle speed and vehicle acceleration. In another aspect, the methodincludes interpolating between at least two vehicle acceleration datapoints and determining the threshold based on the result of theinterpolating step. Moreover, a signal can be sent to an engine controlcircuit to increase the amount of input torque provided to the inputshaft until the countershaft acceleration is within a percentage of thethreshold.

In a different embodiment, a method is provided for controlling inputtorque to a transmission of a powered vehicle. The transmission isoperably powered by an engine. The method includes (a) transferringtorque to an input of the transmission; (b) measuring a rotational speedof a countershaft in the transmission; (c) computing an acceleration ofthe countershaft based on the measured rotational speed; (d) determininga vehicle acceleration threshold based on vehicle speed; (e) comparingcountershaft acceleration to the threshold; and (f) controlling inputtorque based on the result of the comparison.

In this embodiment, the method can include limiting the input torque, orfurthermore, reducing the input torque until the countershaftacceleration is less than the threshold. Similarly, the method can alsoinclude sending a signal to an engine controller to control the inputtorque. Each of the steps in the method can be continuously repeateduntil the countershaft acceleration is less than the threshold.

In another embodiment, a transmission system for a powered vehicle isprovided. The system includes a fluid-coupling device configured toreceive input torque from an engine drive shaft; an input shaft disposedalong a first axis and operably coupled to the fluid-coupling device; anoutput shaft disposed along the first axis and configured to transfertorque to a rear axle of the vehicle; a countershaft disposed along asecond axis, where the first axis and second axis are parallel butspaced from one another; a first sensor, a second sensor, and a thirdsensor, where the first sensor is configured to measure rotational speedof the input shaft, the second sensor is configured to measurerotational speed of the output shaft, and the third sensor is configuredto measure rotational speed of the countershaft; and a controllerdisposed in electrical communication with the first sensor, secondsensor and third sensor. The controller is configured to determinecountershaft acceleration and compare the calculated acceleration to athreshold value. Based on the comparison, the controller is configuredto request an adjustment in the amount of input torque being received bythe fluid-coupling device.

In one aspect of this embodiment, a second countershaft is disposedalong a third axis, where the first axis, second axis, and third axisare each spaced from and parallel to one another. Moreover, a fourthsensor is in electrical communication with the controller, where thefourth sensor is configured to measure rotational speed of the secondcountershaft. In a different aspect, the system further includes a setof instructions readable by the controller, where the instructionsinclude a plurality of data points of acceleration. The controller isconfigured to determine the threshold value from the plurality of datapoints.

An advantage of the present disclosure is the ability to reduce or limittorque to a defined level, or threshold, for purposes of improving fueleconomy. During operation, the transmission controller can monitorcountershaft acceleration and when the acceleration exceeds a definedlevel, the input torque to the transmission can be controlled for fuelsavings. This can be achieved without a vehicle operator or passengerfeeling the difference in torque level. In other words, the transmissioncontroller can communicate with the engine controller to limit inputtorque without notifying or communicating the same to the vehicleoperator.

Another advantage is the integral control of input torque via the engineand transmission. In many conventional vehicle setups, engine power canbe controlled by monitoring vehicle performance. In the presentdisclosure, however, vehicle performance can be better optimized throughthe integrated communication between the engine and transmission.

A further advantage is the use of countershaft acceleration can providereliable and consistent values for monitoring vehicle performance. In atleast one aspect of the present disclosure, the countershaft is arrangedsuch that its rotational acceleration can be monitored reliably comparedto other components in the transmission. This allows for better vehicleperformance and improved fuel efficiency over many conventional setups.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned aspects of the present invention and the manner ofobtaining them will become more apparent and the invention itself willbe better understood by reference to the following description of theembodiments of the invention, taken in conjunction with the accompanyingdrawings, wherein:

FIG. 1 is an exemplary block diagram and schematic view of oneillustrative embodiment of a powered vehicular system;

FIG. 2 is a schematic view of a gear configuration of an automatictransmission having a countershaft;

FIG. 3 is a flowchart of an embodiment for controlling engine torquebased on a transmission characteristic; and

FIG. 4 is an exemplary graph of a vehicle acceleration curve plottedagainst vehicle speed.

Corresponding reference numerals are used to indicate correspondingparts throughout the several views.

DETAILED DESCRIPTION

The embodiments of the present invention described below are notintended to be exhaustive or to limit the invention to the precise formsdisclosed in the following detailed description. Rather, the embodimentsare chosen and described so that others skilled in the art mayappreciate and understand the principles and practices of the presentinvention.

Referring now to FIG. 1, a block diagram and schematic view of oneillustrative embodiment of a vehicular system 100 having a drive unit102 and transmission 118 is shown. In the illustrated embodiment, thedrive unit 102 may include an internal combustion engine, diesel engine,electric motor, or other power-generating device. The drive unit 102 isconfigured to rotatably drive an output shaft 104 that is coupled to aninput or pump shaft 106 of a conventional torque converter 108. Theinput or pump shaft 106 is coupled to an impeller or pump 110 that isrotatably driven by the output shaft 104 of the drive unit 102. Thetorque converter 108 further includes a turbine 112 that is coupled to aturbine shaft 114, and the turbine shaft 114 is coupled to, or integralwith, a rotatable input shaft 124 of the transmission 118. Thetransmission 118 can also include an internal pump 120 for buildingpressure within different flow circuits (e.g., main circuit, lubecircuit, etc.) of the transmission 118. The pump 120 can be driven by ashaft 116 that is coupled to the output shaft 104 of the drive unit 102.In this arrangement, the drive unit 102 can deliver torque to the shaft116 for driving the pump 120 and building pressure within the differentcircuits of the transmission 118.

The transmission 118 can include a planetary gear system 122 having anumber of automatically selected gears. An output shaft 126 of thetransmission 118 is coupled to or integral with, and rotatably drives, apropeller shaft 128 that is coupled to a conventional universal joint130. The universal joint 130 is coupled to, and rotatably drives, anaxle 132 having wheels 134A and 134B mounted thereto at each end. Theoutput shaft 126 of the transmission 118 drives the wheels 134A and 134Bin a conventional manner via the propeller shaft 128, universal joint130 and axle 132.

A conventional lockup clutch 136 is connected between the pump 110 andthe turbine 112 of the torque converter 108. The operation of the torqueconverter 108 is conventional in that the torque converter 108 isoperable in a so-called “torque converter” mode during certain operatingconditions such as vehicle launch, low speed and certain gear shiftingconditions. In the torque converter mode, the lockup clutch 136 isdisengaged and the pump 110 rotates at the rotational speed of the driveunit output shaft 104 while the turbine 112 is rotatably actuated by thepump 110 through a fluid (not shown) interposed between the pump 110 andthe turbine 112. In this operational mode, torque multiplication occursthrough the fluid coupling such that the turbine shaft 114 is exposed todrive more torque than is being supplied by the drive unit 102, as isknown in the art. The torque converter 108 is alternatively operable ina so-called “lockup” mode during other operating conditions, such aswhen certain gears of the planetary gear system 122 of the transmission118 are engaged. In the lockup mode, the lockup clutch 136 is engagedand the pump 110 is thereby secured directly to the turbine 112 so thatthe drive unit output shaft 104 is directly coupled to the input shaft124 of the transmission 118, as is also known in the art.

The transmission 118 further includes an electro-hydraulic system 138that is fluidly coupled to the planetary gear system 122 via a number,J, of fluid paths, 140 ₁-140 _(J), where J may be any positive integer.The electro-hydraulic system 138 is responsive to control signals toselectively cause fluid to flow through one or more of the fluid paths,140 ₁-140 _(J), to thereby control operation, i.e., engagement anddisengagement, of a plurality of corresponding friction devices in theplanetary gear system 122. The plurality of friction devices mayinclude, but are not limited to, one or more conventional brake devices,one or more torque transmitting devices, and the like. Generally, theoperation, i.e., engagement and disengagement, of the plurality offriction devices is controlled by selectively controlling the frictionapplied by each of the plurality of friction devices, such as bycontrolling fluid pressure to each of the friction devices. In oneexample embodiment, which is not intended to be limiting in any way, theplurality of friction devices include a plurality of brake and torquetransmitting devices in the form of conventional clutches that may eachbe controllably engaged and disengaged via fluid pressure supplied bythe electro-hydraulic system 138. In any case, changing or shiftingbetween the various gears of the transmission 118 is accomplished in aconventional manner by selectively controlling the plurality of frictiondevices via control of fluid pressure within the number of fluid paths140 ₁-140 _(J).

The system 100 further includes a transmission control circuit 142 thatcan include a memory unit 144. The transmission control circuit 142 isillustratively microprocessor-based, and the memory unit 144 generallyincludes instructions stored therein that are executable by thetransmission control circuit 142 to control operation of the torqueconverter 108 and operation of the transmission 118, i.e., shiftingbetween the various gears of the planetary gear system 122. It will beunderstood, however, that this disclosure contemplates other embodimentsin which the transmission control circuit 142 is notmicroprocessor-based, but is configured to control operation of thetorque converter 108 and/or transmission 118 based on one or more setsof hardwired instructions and/or software instructions stored in thememory unit 144.

In the system 100 illustrated in FIG. 1, the torque converter 108 andthe transmission 118 include a number of sensors configured to producesensor signals that are indicative of one or more operating states ofthe torque converter 108 and transmission 118, respectively. Forexample, the torque converter 108 illustratively includes a conventionalspeed sensor 146 that is positioned and configured to produce a speedsignal corresponding to the rotational speed of the pump shaft 106,which is the same rotational speed of the output shaft 104 of the driveunit 102. The speed sensor 146 is electrically connected to a pump speedinput, PS, of the transmission control circuit 142 via a signal path152, and the transmission control circuit 142 is operable to process thespeed signal produced by the speed sensor 146 in a conventional mannerto determine the rotational speed of the turbine shaft 106/drive unitoutput shaft 104.

The transmission 118 illustratively includes another conventional speedsensor 148 that is positioned and configured to produce a speed signalcorresponding to the rotational speed of the transmission input shaft124, which is the same rotational speed as the turbine shaft 114. Theinput shaft 124 of the transmission 118 is directly coupled to, orintegral with, the turbine shaft 114, and the speed sensor 148 mayalternatively be positioned and configured to produce a speed signalcorresponding to the rotational speed of the turbine shaft 114. In anycase, the speed sensor 148 is electrically connected to a transmissioninput shaft speed input, TIS, of the transmission control circuit 142via a signal path 154, and the transmission control circuit 142 isoperable to process the speed signal produced by the speed sensor 148 ina conventional manner to determine the rotational speed of the turbineshaft 114/transmission input shaft 124.

The transmission 118 further includes yet another speed sensor 150 thatis positioned and configured to produce a speed signal corresponding tothe rotational speed of the output shaft 126 of the transmission 118.The speed sensor 150 may be conventional, and is electrically connectedto a transmission output shaft speed input, TOS, of the transmissioncontrol circuit 142 via a signal path 156. The transmission controlcircuit 142 is configured to process the speed signal produced by thespeed sensor 150 in a conventional manner to determine the rotationalspeed of the transmission output shaft 126.

In the illustrated embodiment, the transmission 118 further includes oneor more actuators configured to control various operations within thetransmission 118. For example, the electro-hydraulic system 138described herein illustratively includes a number of actuators, e.g.,conventional solenoids or other conventional actuators, that areelectrically connected to a number, J, of control outputs, CP₁-CP_(J),of the transmission control circuit 142 via a corresponding number ofsignal paths 72 ₁-72 _(J), where J may be any positive integer asdescribed above. The actuators within the electro-hydraulic system 138are each responsive to a corresponding one of the control signals,CP₁-CP_(J), produced by the transmission control circuit 142 on one ofthe corresponding signal paths 72 ₁-72 _(J) to control the frictionapplied by each of the plurality of friction devices by controlling thepressure of fluid within one or more corresponding fluid passageway 140₁-140 _(J), and thus control the operation, i.e., engaging anddisengaging, of one or more corresponding friction devices, based oninformation provided by the various speed sensors 146, 148, and/or 150.

The friction devices of the planetary gear system 122 are illustrativelycontrolled by hydraulic fluid which is distributed by theelectro-hydraulic system in a conventional manner. For example, theelectro-hydraulic system 138 illustratively includes a conventionalhydraulic positive displacement pump (not shown) which distributes fluidto the one or more friction devices via control of the one or moreactuators within the electro-hydraulic system 138. In this embodiment,the control signals, CP₁-CP_(J), are illustratively analog frictiondevice pressure commands to which the one or more actuators areresponsive to control the hydraulic pressure to the one or morefrictions devices. It will be understood, however, that the frictionapplied by each of the plurality of friction devices may alternativelybe controlled in accordance with other conventional friction devicecontrol structures and techniques, and such other conventional frictiondevice control structures and techniques are contemplated by thisdisclosure. In any case, however, the analog operation of each of thefriction devices is controlled by the control circuit 142 in accordancewith instructions stored in the memory unit 144.

In the illustrated embodiment, the system 100 further includes a driveunit control circuit 160 having an input/output port (I/O) that iselectrically coupled to the drive unit 102 via a number, K, of signalpaths 162, wherein K may be any positive integer. The drive unit controlcircuit 160 may be conventional, and is operable to control and managethe overall operation of the drive unit 102. The drive unit controlcircuit 160 further includes a communication port, COM, which iselectrically connected to a similar communication port, COM, of thetransmission control circuit 142 via a number, L, of signal paths 164,wherein L may be any positive integer. The one or more signal paths 164are typically referred to collectively as a data link. Generally, thedrive unit control circuit 160 and the transmission control circuit 142are operable to share information via the one or more signal paths 164in a conventional manner. In one embodiment, for example, the drive unitcontrol circuit 160 and transmission control circuit 142 are operable toshare information via the one or more signal paths 164 in the form ofone or more messages in accordance with a society of automotiveengineers (SAE) J-1939 communications protocol, although this disclosurecontemplates other embodiments in which the drive unit control circuit160 and the transmission control circuit 142 are operable to shareinformation via the one or more signal paths 164 in accordance with oneor more other conventional communication protocols (e.g., from aconventional databus such as J1587 data bus, J1939 data bus, IESCAN databus, GMLAN, Mercedes PT-CAN).

Referring to FIG. 2, an embodiment of an exemplary transmission 200 isshown. The transmission 200 can be arranged to include a plurality ofcenterlines defined between an input and output thereof. For instance, afirst centerline 202 is defined such that an input shaft 208 and outputshaft 210 are disposed thereon. The input shaft 208 can be operablycoupled to a fluid coupling device such as a torque converter (notshown). The transmission 200 can further include a second centerline 204and a third centerline 206. A first countershaft 212 can be arrangedalong the second centerline 204 and a second countershaft 214 can bearranged along the third centerline 206.

In this embodiment, the input shaft 208 and first countershaft 212 canbe coupled to one another by a pair of torque-transmitting devices 216,218 (e.g., meshing gears). Similarly, the input shaft 208 and secondcountershaft 214 can be coupled to one another by a different pair oftorque-transmitting devices 220, 222 (e.g., meshing gears). As analternative, sprocket assemblies can be used instead of meshing gearsfor coupling the input shaft 208 to the first countershaft 212 andsecond countershaft 214. A third pair of torque-transmitting devices224, 226 (e.g., meshing gears) and a fourth pair of torque-transmittingdevices 228, 230 (e.g., meshing gears) can further couple the inputshaft 208 to the first countershaft 212 and second countershaft 214,respectively, depending on which clutch assemblies are applied.

In FIG. 2, the transmission 200 can include a plurality of clutchassemblies (e.g., wet clutches, dry clutches, dog clutches, brake discs,etc.). In this disclosed embodiment, the transmission 200 includes afirst clutch assembly 232, a second clutch assembly 234, a third clutchassembly 236, a fourth clutch assembly 238, a fifth clutch assembly 240,a sixth clutch assembly 242, and a seventh clutch assembly 244. In otherembodiments, there can be additional or fewer clutch assemblies. In thepresent disclosure, there can be any number and type of clutchassemblies.

During transmission operation, the rotational speed of the input shaft208, output shaft 210, and countershafts 212, 214 can be measured. Inone embodiment, the first countershaft 212 and second countershaft 214can rotate at about the same speed. In another embodiment, thecountershafts can rotate at different speeds. In a further embodiment,the first countershaft 212 and second countershaft 214 can rotate atabout the same speed or at different speeds depending on the gear ratio.To measure input shaft speed, a sensor 246 is provided. Likewise, outputshaft speed can be measured by another sensor 248 located proximate theoutput shaft 210. The sensors 246, 248 can be similar to any one of thespeed sensors 146, 148, and 150 in FIG. 1. The sensors 246, 248 can becoupled to an outer housing of the transmission 200 or disposedinternally of the outer housing. The countershaft speeds can be measuredby a third sensor 250 which is positioned near the second clutchassembly 234.

Each of the sensors 246, 248, 250 can be electrically coupled to atransmission control circuit similar to the one in FIG. 1 (e.g., circuit142). Thus, the control circuit can communicate with the sensors andperform functions based on such communication. Further, the controlcircuit can be electrically coupled to an engine control circuit (e.g.,drive unit control circuit 160) for communicating back and forth. Inthis disclosure, the transmission control circuit can receive signalsfrom the sensors 246, 248, 250 and perform an action includingcommunicating with the engine control circuit to control engine andtransmission performance.

In FIG. 3, an exemplary method 300 of controlling input torque to atransmission is provided. In block 302, the rotational speed of thecountershaft is measured by a speed sensor. Referring to FIG. 2, forexample, the sensor 250 is positioned to measure the rotational speed ofthe first countershaft 212 and second countershaft 214. Once thecountershaft speed is measured, the sensor 250 can send a signal to thetransmission controller 104 with the measured speed. The sensor 250 cancontinuously measure the countershaft speed and repeatedly send signalsto the transmission controller with the measurements. Moreover, as isthe case in FIG. 2 with two or more countershafts, there may be aplurality of countershaft speed sensors 250 disposed in or on thetransmission to measure the rotational speed of each countershaft. Eachspeed sensor 250 can be in electrical communication with thetransmission control circuit such that each countershaft speed isreceived by the transmission control circuit in block 302.

In block 304, the transmission controller 104 can calculate countershaftacceleration based on the repeated countershaft speed measurements sentby the sensor 250. Countershaft acceleration can be computed accordingto any known, conventional manner. For instance, over a time period ofcollecting countershaft rotational speed measurements, the accelerationcan be computed according to known means. Similar to countershaft speedmeasurements, the transmission control circuit 104 can repeatedlycalculate countershaft acceleration.

As the transmission control circuit continuously computes thecountershaft acceleration, a signal containing current vehicle speeddata can be provided to the transmission control unit in block 306.Vehicle speed can be provided over a datalink or databus as describedabove. Alternatively, it can be measured by a vehicle speed sensormounted to the vehicle.

In block 308, once the vehicle speed is known, the transmission controlcircuit can determine a threshold value based on vehicle speed. In oneembodiment, a software program downloaded to and readable by thetransmission control circuit includes threshold values. The thresholdvalues can be arranged in one or more tables, graphically, or in anotherformat. The threshold can be determined based on the vehicle speed andcalculated countershaft acceleration. A non-limiting example of this isprovided in FIG. 4.

In FIG. 4, a graphical representation 400 is provided to illustrate themanner in which the threshold value is obtained in block 308. In thisrepresentation 400, vehicle acceleration is plotted against vehiclespeed and a curve 402 is shown. The curve 402 can represent a preferredor desired acceleration curve for purposes of fuel economy and/orvehicle performance. The curve 402 can have any desired shape dependingon its use. Moreover, there can be two or more such curves depending onvarious conditions (e.g., vehicle performance, road conditions, vehicleload, etc.).

In a different embodiment, the vehicle speed and vehicle accelerationdata can be arranged in a tabular format rather than a graphical format.The transmission control circuit can interpolate between values in oneor more of the tables for determining the threshold value. The thresholdvalue can be defined as an acceleration value.

In block 310, the countershaft acceleration that is calculated in block304 can be compared to the threshold value obtained in block 308. To doso, the countershaft acceleration value is compared to the vehicleacceleration values, for example, in the graphical representation 400 ofFIG. 4. The transmission control circuit uses the vehicle speed andcountershaft acceleration to determine how the calculated countershaftacceleration compares to the curve 402. In a first, non-limitingexample, the countershaft acceleration may be calculated as a first datapoint 404. In this example, the countershaft acceleration is below thecurve 402. As such, the transmission control circuit can requestadditional input torque from the engine or drive unit withoutsubstantially affecting fuel efficiency. In other words, the amount ofinput torque being transferred to the transmission has not exceeded athreshold limit which would cause the countershaft to accelerate at arate that is detrimental to fuel economy. The transmission control unitcan either request additional input torque, or the transmission controlunit can remain idle and allow the engine or drive unit to continueproducing the same amount of torque.

In an alternative example, the countershaft acceleration may becalculated at a second data point 406. In this instance, thecountershaft acceleration actually exceeds a desirable limit (e.g., isshown above the curve 402 in FIG. 4). The transmission control unit candetermine this and take appropriate action, including but not limited tosending a signal to an engine control unit to limit or reduce inputtorque (block 312). In one aspect, it may be desirable to reduce inputtorque until the countershaft acceleration is less than the threshold.In a different aspect, it may be desirable to reduce input torque to apercentage (e.g., 90%) of the desired or maximum acceleration.

If the transmission control circuit has data points in the form oftabular data, the control circuit can calculate countershaftacceleration and compare the calculated result to the data points in theone or more tables. In the event the calculated countershaftacceleration falls between two threshold data points, the controller 104can interpolate in block 308 to determine the threshold value. Aspreviously described, the controller 104 can perform the functions ofblocks 310 and 312 once the threshold value is determined.

In the embodiment of FIG. 2, the countershaft speed can be a ratio ofthe input shaft speed. In an embodiment in which the sensor 250 is notprovided or malfunctions, the controller can calculate countershaftspeed. For instance, the countershaft speed can be calculated as theproduct of an output splitter gear ratio and measured output shaftspeed. Alternatively, the countershaft speed can be computed as theproduct of the output splitter gear ratio, the current transmission gearratio, and the input shaft speed.

In one non-limiting embodiment, the transmission 200 can shift betweenat least ten different forward ranges and two reverse ranges. In atleast two different forward ranges, the sixth clutch assembly 242 isapplied in one of the ranges and the seventh clutch assembly 244 isapplied in the other. The sixth and seventh clutch assemblies can forman output assembly range clutch pack. When the transmission shiftsbetween the aforementioned forward ranges, e.g., when one of the sixthand seventh clutch assemblies is unapplied and the other is applied, theresulting countershaft speed is proportional to the gear ratio of theoutput assembly range clutch pack.

In many instances, countershaft acceleration is an easier calculationand transmission characteristic to use for controlling vehicle andtransmission performance. In particular, countershaft acceleration canbe substantially easier to control compared to input shaft acceleration,and thus it is one advantage of the present disclosure. The input shaftacceleration, and in particular input shaft speed, can often changerapidly through each transmission gear shift during operation.Alternatively, in many embodiments, the countershaft speed does notchange rapidly other than during a single shift (e.g., between a shiftfrom a fifth range to a sixth range). In one exemplary embodiment, thetransmission 200 can shift between eight or more ranges, and at leastduring vehicle launch, the shifts occur frequently between a first rangeand a higher range that acceleration control needs to operate in anopen-loop mode if using input shaft speed as feedback. This can often bedifficult to control, particularly when it is desired to maintain orachieve desired fuel economy and vehicle performance.

While exemplary embodiments incorporating the principles of the presentinvention have been disclosed hereinabove, the present invention is notlimited to the disclosed embodiments. Instead, this application isintended to cover any variations, uses, or adaptations of the inventionusing its general principles. Further, this application is intended tocover such departures from the present disclosure as come within knownor customary practice in the art to which this invention pertains andwhich fall within the limits of the appended claims.

What is claimed is:
 1. A transmission system for a powered vehicle,comprising: a fluid-coupling device configured to receive input torquefrom an engine drive shaft; an input shaft disposed along a first axisand operably coupled to the fluid-coupling device; an output shaftdisposed along the first axis and configured to transfer torque to arear axle of the vehicle; a countershaft disposed along a second axis,where the first axis and second axis are parallel but spaced from oneanother; a first sensor, a second sensor, and a third sensor, where thefirst sensor is configured to measure rotational speed of the inputshaft, the second sensor is configured to measure rotational speed ofthe output shaft, and the third sensor is configured to measurerotational speed of the countershaft; and a controller disposed inelectrical communication with the first sensor, second sensor and thirdsensor; wherein, the controller is configured to determine countershaftacceleration and compare the calculated acceleration to a thresholdvalue; further wherein, based on the comparison, the controller isconfigured to request an adjustment in the amount of input torque beingreceived by the fluid-coupling device.
 2. The system of claim 1, furthercomprising: a second countershaft disposed along a third axis, where thefirst axis, second axis, and third axis are each spaced from andparallel to one another; and a fourth sensor being in electricalcommunication with the controller, where the fourth sensor is configuredto measure rotational speed of the second countershaft.
 3. The system ofclaim 1, further comprising a set of instructions readable by thecontroller, where the instructions include a plurality of data points ofacceleration; wherein, the controller is configured to determine thethreshold value from the plurality of data points.